It has been reported in U.S. Pat. Nos. 6,800,660; 6,762,204; 7,037,940; 7,001,923; and 6,924,312 that certain bis (thio-hydrazide amide) compounds significantly enhance the anti-cancer activity of paclitaxel and paclitaxel analogs. In particular, N-malonyl-bis(N′-methyl-N′-thiobenzoylhydrazide) in combination with taxol has been shown to increase the time to progression of patients suffering from stage IV metastatic melanoma relative to patients treated with paclitaxel alone. It would be advantageous to have crystalline forms of N-malonyl-bis(N′-methyl-N′-thiobenzoylhydrazide) having properties that are suitable for large-scale manufacture (e.g., dry powder fill) of the compound as a drug.